US President Donald Trump has announced sweeping tariffs on global trade, adding taxes of as much as 50% to imports from some countries.

The tariffs, he says, are “reciprocal” – calculated to address currency manipulation and trade barriers that other countries place on the US.

However, when you look at how the new tariffs were actually calculated, that claim does not add up.

Tim Harford speaks to Thomas Sampson, an associate professor at the London School of Economics, to understand what is going on.

Presenter: Tim Harford